1. Field of the Invention
The present invention relates to a multi-layer magnetooptical recording medium capable of overwriting with magnetic field modulation method.
2. Related Background Art
Efforts are being recently made toward the development of an optical record/reproducing method satisfying various requirements including a high density, a high capacity, a high access speed and a high recording and reproducing speed, and a recording apparatus, a reproducing apparatus and a recording medium adapted for use in such method.
Among various optical record/reproducing methods, the magnetooptical method is most attractive due to its unique advantage of ability to erase the information after the recording and reproduction thereof and to repeat this process by any number of times.
The recording medium employed in said magneto-optical record/reproducing method is provided, as the recording layer, with a perpendicular magnetic layer or layers. Said layer is composed, for example, of amorphous GdFe, GdCo, GdFeCo, TbFe, TbCo or TbFeCo. The recording layer generally constitutes a concentric, spiral or linear track, on which information is recorded. In the present text, either of "upward" and "downward" directions with respect to the surface of the layer is defined as "direction A", and the other as "inverse direction A". The information to be recorded is binarized in advance, and recorded by a mark B.sub.1 having magnetization of "direction A" and a mark B.sub.0 having magnetization of "inverse direction A". Each mark represents a bit, and said marks B.sub.1 and B.sub.0 correspond to "1" and "0" of binary signal. Prior to the recording, the magnetization of the track for information recording is aligned to the state B.sub.0 of "inverse direction A" by the application of a strong external magnetic field, and this process is called "initialization". Then the marks B.sub.1 of the "inverse direction A" according to the information signal to be recorded. The information is recorded by the combination of binary marks B.sub.0 and B.sub.1.